The present invention relates to a recording material for ink-jet printing process. In particular, the invention is concerned with an ink-jet recording material that can ensure very excellent light-resistant properties in images recorded therein and can provide images of excellent coloration quality when ink-jet printing in color is done thereon by the use of not only dye ink but also pigment ink.
Ink-jet recording methods can easily achieve full-color recording and reduction of printing noises. In recent years, therefore, the utilization of ink-jet recording methods has been spreading at a rapid rate. According to such a method, fine drops of ink are jetted from nozzles at a high speed so as to direct toward a recording material, and a large quantity of solvent is contained in the ink used. As a result, recording materials for ink-jet recording are required to absorb ink promptly.
The recent years have also seen rapid proliferation of personal computers and digital cameras. Under these circumstances, printers as apparatus for outputting such digital image information have come to be required to produce images having qualities on a level similar to those attained by silver salt photography. Thus, it has also become necessary for ink-jet recording materials used in such printers to ensure colors of higher densities, higher resolution and more excellent color reproduction than usual in the images printed thereon.
On the other hand, the storage stability of recorded images has come to assume greater importance as significant improvements in image quality have been made. In the ink-jet process, acid dyes and direct dyes have been prevailingly used in printing ink, because they cause no clogging of a printing head and provide color images of high saturation. Under current circumstances, therefore, it is not always possible to choose dyes having satisfactory water resistance and light resistance For the purpose of ensuring both water resistance and light resistance for printed images, Tokkai Sho 59-198188 (the term xe2x80x9cTokkaixe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent application) discloses the use of specified cationic resins, such as quaternary compounds of polyethylenimine, in the ink-receiving layer of an ink-jet recording material, Tokkai Sho 60-260377 discloses the use of cationic colloidal silica, Tokkai Sho 61-146591 discloses the use of hindered amine compounds, and Tokkai Sho 61-284478 discloses the use of quaternary ammonium salts of polyoxyalkylenated amine monocarboxylic acid esters.
However, the use of those compounds cannot impart sufficient light resistance to printed images, although it is certain that appreciable improvements in water resistance are observed. Such being the case, ink-jet recording materials successful in attaining compatibility between water resistance and light resistance have not been developed yet.
As to improvement of light resistance, it is disclosed to add an ultraviolet absorbent and an antioxidant to recording layers in Tokkai Sho 57-87988 and Tokkai sho 57-87989 respectively. Although the light resistance is improved for a certainty by addition of such agents, the improvement achieved is still insufficient from the practical point of view, and besides, the added agents create problems of printed image quality. More specifically, serious reduction in color densities of printed images is caused in the former case, so the printed images cannot have qualities comparable to those of photographs from the very beginning of a printing operation. In the latter case, on the other hand, the antioxidant itself turns brown with a lapse of time, so the keeping quality in white areas of recording paper becomes a problem.
As mentioned above, traditional arts cannot provide ink-jet recording materials capable of forming images comparable to photographic images in appearance and, what is more, retarding deterioration caused in image quality by exposure to light, water or gas, and being free of discoloration in the white areas, namely having high keeping quality.
More specifically, the addition of chemicals for improvement of keeping quality to a recording layer or the formation of a protective layer containing such chemicals on a recording layer in ordinary manners cannot bring about desirable results. After all, it is impracticable to form a protective layer outside the ink-receiving layer since the ink-jet recording process consists in forming images by directing a jet of ink at the recording layer surface. In addition, the coloring materials used for the ink are direct dyes and acid dyes. Although these dyes are superior in hue, they are liable to discolor or lose their colors through cleavage of the double bonds in the dye structures by ultraviolet rays or oxidative gases. In addition, they are susceptible to other chemical reagents also, and so the addition of chemical reagents to the coloration layer tends to produce negative effect directly on coloration.
As a result of intensive study to solve those difficulties, to our surprise, we have found that the addition of a light resistance-imparting chemical prepared by mixing 1 to 10 parts by weight of an ultraviolet absorbent of benzotriazole type, 1 to 8 parts by weight of magnesium sulfate and 1 to 10 parts by weight of zinc oxide to a layer arranged just under a coloration layer to receive ink directly can produce significant improvement in light resistance, and besides, can completely preclude negative influences of chemicals on coloration of dyes, which has so far been a problem in need of solution, thereby achieving the present invention.
Therefore, an object of the invention is to provide a recording material on which images having high color density, excellent color reproduction and photographic quality can be printed, particularly by means of a high-resolution ink-jet printer, and besides, the images printed have excellent light resistance and undergo no changes in hue upon storage.
The aforementioned object is attained with an ink-jet recording material having on a support at least an ink-receiving layer, characterized in that the ink-receiving layer is comprised of a light resistance-imparting layer as a lower layer and a coloration layer as an upper layer, the light resistance-imparting layer comprises 100 parts by weight of ink absorbing pigments, and a light resistance-imparting chemical constituted of 1 to 10 parts by weight of a benzotriazole ultraviolet absorbent, 1 to 8 parts by weight of magnesium sulfate and 1 to 10 parts by weight of zinc oxide, and the coloration layer is a layer free of light resistance-imparting chemicals.
Further, it has been ascertained that the present recording material ensured more excellent coloration than ever in images printed with pigment ink as well as dye ink.
The major function of the present coloration layer consists in receiving ink and fixing dyes in ink to form ink images therein. The specific composition of this layer may be selected appropriately from those of hitherto known ink-receiving layers depending on the intended quality level of images; however, it is of primary importance to the invention to formulate the coloration layer so to be free of light resistance-imparting chemicals. As suitable examples of ingredients mainly constituting the coloration layer, mention may be made of a pigment having high oil absorption, that is, high ink receptivity, a binder for the pigment and a cationic high polymer capable of fixing dyes and enhancing water resistance. The coloration layer may be a single layer or a multiple layer.
The main function of the present light resistance-imparting layer consists in absorbing and fixing a vehicle of ink passing through the coloration layer. Therefore, it is appropriate that the light resistance-imparting layer be constituted mainly of a pigment having high oil absorption and a binder for the pigment, although the composition thereof should be selected depending on the kind of ink to be used and the recording speed to be set. The key feature of the invention is incorporation of light resistance-imparting chemicals into this light resistance-imparting layer as a lower layer of the coloration layer.
The light resistance-imparting chemicals may be incorporated through addition to a coating composition together with the pigment and the binder. In another way, a solution containing these chemicals as main components may be coated on a layer made up of the pigment and the binder, or the layer may be immersed in the solution. Further, the light resistance-imparting layer may be a single layer or a multiple layer.
In addition, a coating layer participating in ink absorption may be provided between the light resistance-imparting layer and the support.
The suitable coverage of each coating layer depends on the kind of ink used, the minuteness level of the intended images, the recording speed, the kinds and the formulation of ingredients constituting the layer.
With respect to the coloration layer, the suitable coverage is generally from 3 to 30 g/m2, preferably from 4 to 15 g/m2. Decrease in coverage of the coloration layer tends to cause degradation in ink absorption, while increase therein tends to adversely affect light resistance. As far as the coloration layer has its coverage in the aforementioned range, it can hold a relatively low concentration of ink-jet printing ink in an amount required for formation of photograph-like images, and besides, the effects of light resistance-imparting chemicals incorporated in the absorbing layer provided underneath the coloration layer can be achieved.
The suitable coverage of the light resistance-imparting layer, though it somewhat depends on the kind of base paper used, ranges roughly from 3 to 30 g/m2, preferably from 4 to 20 g m2. The light resistance-imparting layer having a low coverage tends to lower ink absorption and light resistance; while the light resistance-imparting layer having a high coverage tends to be weak in coating layer strength and have a disadvantage of high cost.
Further, it is advantageous that the total coverage of the coloration layer and the light resistance-imparting layer is from 6 to 30 g/m2. When the coverage is less than 6 g/m2, the ink-receiving layer as a whole causes a shortage of ink-absorbing capacity; as a result, a bleeding phenomenon may occur. When the total coverage is increased beyond 30 g/m2, on the other hand, reduction in coating layer strength tends to be caused; as a result, the coatings are liable to come off in powder. In addition, such a great coverage causes a too large increase of ink absorption in the vertical direction; as a result, the diameter of ink dots becomes too small to completely fill up solid images, and the so-called banding phenomenon tends to occur.
The light resistance-imparting chemical used in the invention is a combination of zinc oxide as inorganic ultraviolet absorbent, a benzotriazole compound as organic ultraviolet absorbent and magnesium sulfate as a metal salt. On the other hand, titanium dioxide and cerium oxide well-known as inorganic ultraviolet absorbents are unsuitable for the present purpose, because these oxides sometimes do light resistance more harm than good when used in the present ink-receiving layer.
The amount of zinc oxide added is from 1 to 10 parts by weight, particularly preferably 2 to 8 parts by weight, per 100 parts by weight of ink-absorptive pigment. When zinc oxide is added in an amount smaller than 1 parts by weight, it cannot impart satisfactory light resistance; while, when the amount of zinc oxide added is greater than 10 parts by weight, the images formed take on a undesirable yellowish hue.
Further, ultraviolet absorbents of benzophenone and hindered amine types, which are well-known as organic ultraviolet absorbents, require addition in greater amounts because their contributions to light resistance-increasing effect are small. As a result, the production cost becomes high and their adverse influences on printed image quality, including ink absorption and coloration, come to be not negligible, so their use is not practical.
The amount of benzotriazole compound mixed as organic ultraviolet absorbent is from 1 to 10 parts by weight, preferably from 2 to 8 parts by weight, per 100 parts by weight of ink-absorptive pigments. When the benzotriazole compound as ultraviolet absorbent is used in an amount smaller than 1 parts by weight, the intended light resistance cannot be attained; while, when it is used in an amount greater than 10 parts by weight, it renders the coating layer opaque to degrade coloration of ink. The organic ultraviolet absorbent used in the invention may be any of benzotriazole compounds as far as they have at least one benzotriazole nucleus per molecule and ultraviolet absorbing properties. However, as suitable examples thereof, mention may be made of 2-(2xe2x80x2-hydroxy-5xe2x80x2-methylphenyl)benzotriazole, 2-(2xe2x80x2-hydroxy-5xe2x80x2-t-octylphenyl)benzotriazole, 2-(2xe2x80x2-hydroxy-3xe2x80x2-t-butyl-5xe2x80x2-methylphenyl)-5-chlorobenzotriazole, 2-(2-hydroxy-3xe2x80x2, 5xe2x80x2-di-t-butylphenyl)-5-chlorobenzotriazole, 2-(2xe2x80x2-hydroxy-3xe2x80x2, 5xe2x80x2-di-t-amylphenyl)benzotriazole and methylene-bis[2-(2xe2x80x2-hydroxy-5xe2x80x2-dodecanylphenyl)benzotriazole].
By mixing magnesium sulfate in the present light resistance-imparting layer, images formed in the present recording material can have more improved light resistance. In particular, the magnesium sulfate mixed can produce significant improvement in light resistance of a magenta image hitherto inferior to those of other color images. Although reasons why the light resistance of color images can be improved by magnesium sulfate are unclear yet, the light resistance improvement may be supposed to be due to stabilization of coloring materials in ink by magnesium sulfate. On the other hand, the use of water-soluble metal salts other than magnesium sulfate causes problems. For instance, the use of aluminum salts causes a bronze phenomenon, or reddish coloration of black image. In the case of using sodium salts, the effect produced is insufficient. When zinc salts are used, on the other hand, the images formed come to assume a yellowish tint with the lapse of time.
The amount of magnesium sulfate mixed is from 1 to 8 parts by weight, particularly preferably from 2 to 6 parts by weight, per 100 parts by weight of ink-absorptive pigments. When the amount of magnesium sulfate mixed is smaller than 1 parts by weight, satisfactory light resistance cannot be achieved. Therein, discoloration of magenta ink is serious in particular. When the amount of magnesium sulfate mixed is greater than 8 parts by weight, on the other hand, undesirable bronze phenomenon is observed.
The present recording material has no particular restrictions on a support used therein. Both transparent and opaque supports can be used therein. Examples thereof include various plastic films, such as films of cellophane, polyethylene, polypropylene, soft polyvinyl chloride, hard polyvinyl chloride and polyester, and a wide variety of paper, such as wood-free paper, base paper for photographic paper, drawing paper, painting paper, art paper, coated paper, cast-coated paper, craft paper, impregnated paper and synthetic paper. Depending on the desired purpose, the support for the present recording material can be selected properly from the plastic films or various paper sheets as recited above.
The pigment generally used in the present light resistance-imparting layer and coloration layer is synthetic amorphous silica, but other pigments may also be used. Examples of usable pigments include alumina, hydrated alumina (e.g., alumina sol, colloidal alumina and psuedo-boehmite), aluminum silicate, magnesium silicate, magnesium carbonate, precipitated calcium carbonate, ground calcium carbonate, kaolin, talc, calcium sulfate, zinc carbonate, calcium silicate and aluminum hydroxide, and plastic pigments.
For attaining the intended ink absorbency as the coverage is kept within a range that the coating layers don""t come off in powder after drying, the pigments used are required to have an average oil absorption high to a certain extent. Specifically, it is advantageous for the pigments used to have their average oil absorption within the range of 100 to 300 ml/100 g.
The foregoing oil absorption expressed as an average indicates that, even when a mixture of two or more pigments having different oil absorption values is used, the mixture can serve for the purpose as far as the average of oil absorption values for all the pigments mixed is within the foregoing range. The light resistance-imparting layer and the coloration layer may be identical in species and amounts of pigments mixed, but it is advantageous that the average oil absorption of pigments used in the coloration layer is a little higher than that in the light resistance-imparting layer. Additionally, the oil absorption is determined by the method defined in JIS K5101. The binder used in the present light resistance-imparting layer and the coloration layer each can be selected appropriately from known binders, such as polyvinyl alcohol and modified products of polyvinyl alcohol, polyvinyl acetate, oxidized starch, etherified starch, casein, gelatin, soybean protein, carboxymethyl cellulose, SB latex, NB latex, acrylic resin latex, ethylene-vinyl acetate copolymer latex, polyurethane and unsaturated polyester resins. These binders may be used alone or as a mixture thereof. Although the suitable amount of binders used somewhat varies depending on pigments used in combination, the range thereof is limited. Specifically, the suitable amount of binders added is in the range of 5 to 60 parts by weight, preferably 10 to 40 parts by weight, per 100 parts by weight of pigments used in combination.
This is because, when the amount of binders used is smaller than 5 parts by weight, the coating layer is low in strength irrespective of species of pigments used, and so it tends to come off in powder and has a surface-strength problem. On the other hand, when the amount of binders used is increased beyond 60 parts by weight, the ink absorption of the resulting layer is degraded, and so bleeding or setoff problems tend to arise.
To the light resistance-imparting layer and the coloration layer according to the invention, various additives including a pigment-dispersing agent, a thickener, an antifoaming agent, a defoaming agent, a release agent, a blowing agent, a coloring dye, a coloring pigment, a fluorescent dye, an antiseptic, a waterproof agent, a surfactant and a wet paper strength increasing agent can be added in appropriate amounts, if needed.
For providing the present light resistance-imparting and coloration layers on a support, general coating apparatus of various kinds, such as a blade coater, a roll coater, an air knife coater, a bar coater, a gate roll coater, a curtain coater, a short dwell coater, a gravure coater, a flexo gravure coater and a size press, can be used under an on-machine or off-machine condition. In addition, a transfer method can also be adopted wherein the light resistance-imparting layer is coated on a support, the coloration layer is coated on a film, and then these coatings are brought into face-to-face contact and bonded together. Further, it is also possible to produce a high-gloss recording material by coating a coloration layer by means of a cast coater after providing the light resistance-imparting layer. Furthermore, surface treatment with a calendering apparatus, such as a machine calender, a super calender or a soft calender, may be carried out after providing the coloration layer. Of course, such surface treatment may be carried out at the stage of providing the light resistance-imparting layer, then a coloration layer is provided, and such surface treatment may be carried out once again.
The entire disclosure of all application, patents and publications, cited above and below, and of corresponding Japanese applications No. 2000-219159, filed Jul. 19, 2000 and No. 2001-216204, filed Jul. 17, 2001, are hereby incorporated by reference.
Now, the invention is illustrated in more detail by reference to the following examples. However, it should be understood that these examples are not to be construed as limiting the scope of the invention in any way. Unless otherwise noted in the following examples and comparative examples, all xe2x80x9cpartsxe2x80x9d and all xe2x80x9c%xe2x80x9d are by weight and the term xe2x80x9ccoveragexe2x80x9d is expressed as a dry weight (g) per m2 of coating layer. Additionally, formulae of coating compositions prepared in Examples and Comparative Examples are set forth in Table 1, and the results obtained are shown in Table 2.